1. Field of the Invention
The present invention relates to a tape loading apparatus for use with a rotary magnetic head type recording and/or reproducing apparatus, such as, a video tape recorder.
2. Description of the Prior Art
In a known video tape recorder (VTR) employing a tape cassette, a tape loading operation is performed in which a tape 8 is withdrawn from a tape cassette 1 and is then wrapped around a rotary head drum 9, as shown in FIGS. 1A and 1B.
When the tape cassette 1 is loaded onto a VTR (not shown), as shown in FIG. 1A, loading guides 3, 4 and 5 suitably movable in response to rotation of a loading ring 2 are disposed in a tape withdrawing position. Then, a motor 6 drives a worm gear assembly 7 to rotate the loading ring 2 in the direction indicated by an arrow L and, in response thereto, loading guides 3, 4 and 5 act to withdraw a tape 8 from the tape cassette 1, and to wrap the withdrawn tape around the rotary drum 9 with a predetermined wrap angle, for example, 180.degree. as shown in FIG. 1B, and the loading operation is ended. At the completion of the loading operation, the tape is proximate to a pinch roller 10 and a capstan 11, as also shown on FIG. 1B.
During such loading, rotation of a supply reel 12 in the tape cassette 1 is precluded by a braking force applied thereto, and a take-up reel 13 has a constant torque applied thereto in the direction resisting unwinding of the tape therefrom. In this state, the loading ring 2 is rotated at a predetermined speed to withdraw the tape 8 from the take-up reel 13 and, in response to such rotation of the ring 2, the first to third guides 3 to 5 are sequentially operated to bring the withdrawn tape 8 to the predetermined loading position shown in FIG. 1B.
Due to the somewhat irregular movements of the loading guides 3, 4 and 5 in the course of the tape loading operation and the sudden stop of the tape 8 at the completion of the loading operation or the like, the tape withdrawing speed from the tape cassette may be presented by the solid line in FIG. 2B. Meanwhile, the amount of the tape 8 withdrawn from the tape cassette 1 changes, for example, as shown by a solid line in FIG. 2A.
In the prior art, the rotating speed of the loading ring 2 is constant during the loading operation so that there are sharp changes in the tape withdrawing speed, as represented by steeply inclined portions of the solid line on FIG. 2B.
When the tape cassette 1 is large in size, the inertia of the take-up reel 13 cannot be neglected. Thus, if the torque applied to the take-up reel 13 is constant for resisting unwinding of tape therefrom during each loading operation, there are encountered the following problems.
When the withdrawing speed of the tape 8 is decreased as shown by the solid line in FIG. 2B, if the change in the rotating speed of the take-up reel 13 determined by the inertia of the take-up reel 13 and the torque applied thereto and the change in the tape withdrawing speed are similar, the tape tension is always constant and hence there is no problem. However, the inertia of the take-up reel 13 is increased with the increase of the radius of the tape 8 wound on the take-up reel 13. If the torque applied to the take-up reel 13 is constant, the rate of change in the rotating speed of the take-up reel 13 is changed in response to an increased inertia thereof upon a sudden decrease in the withdrawing speed of the tape. More particularly, if the radius of the tape 8 wrapped on the take-up reel 13 is large, and hence the inertia of the take-up reel 13 is large, the rotating speed of the take-up reel 13, as represented by the broken line in FIG. 2B, changes relatively slower as compared with the rapid change of the tape withdrawing speed, thus causing the withdrawn tape 8 to be slackened. The amount by which the withdrawn tape 8 is slackened increases with the radius of the tape 8 wrapped on the take-up reel 13. In the worst cases, the tape 8 may slip off the loading guides. Further, at the end of the loading operation, tension is suddenly applied to the slackened tape 8 and the tape 8 will be damaged thereby. This risk occurs when the loading ring 2 is fully stopped at the completion of the loading operation and the torque applied to the take-up reel to resist unwinding therefrom, is then effective to suddenly tension the previously slackened tape.